The present invention relates to a method and an apparatus for positioning a disk-shaped object in a predetermined position and orientation.
For example, a reaction chamber is used to form an electrode pattern on the surface of a semiconductor wafer by plasma dry etching. This processing operation is a minute and delicate one, in which a wafer is held on an electrode in a reaction chamber, for example, by electrostatic attraction, vacuum is produced in the reaction chamber and plasma gas is generated, and heat transfer gas such as He gas is supplied onto the back surface of the wafer facing the electrode to keep the temperature, by which the operation is performed. In order to achieve such an operation with required accuracy, the wafer must be placed on the electrode with high positional accuracy. In many cases, since the wafer has a disk shape, the position of its center becomes a problem. Also, since the wafer is a single crystal, the electrode pattern or the like must be formed corresponding to the orientation of the crystal. Therefore, the positioning necessary for the aforesaid operation must be performed with regard to the position of the wafer center and the orientation around the center.
To position such a disk-shaped object with regard to the center position and orientation thereof, a notch b, which is an orientation flat (straight cut portion) or a notch indicating the orientation of a disk-shaped object a, is formed at the outer periphery of the disk-shaped object a as shown in FIG. 6. After this disk-shaped object a is placed on a rotating stage c, the rotating stage c is moved together with a rotating mechanism d in two directions of X and Y perpendicular to each other by using an X-direction moving table e and a Y-direction moving table f, by which the center position of the disk-shaped object a is positioned at a predetermined position. To orient this disk-shaped object a, whose center has been positioned, around the center thereof, the rotating stage c is turned by the rotating mechanism d such as a motor so that the notch b formed in the disk-shaped object a is oriented in a predetermined direction. In positioning, the center position of the disk-shaped object a is judged by detecting about three points of outer periphery of the disk-shaped object a by using a range-finding sensor g, and the rotating stage c is moved so that the judged center position becomes the predetermined position. The orientation of the disk-shaped object a, whose center has been positioned, is judged by detecting the direction of the notch b by using the range-finding sensor g, and the rotating stage c is turned so that the detected direction becomes the predetermined direction. The above described positioning mechanism is usually formed into a unit. In positioning in the atmosphere, this unit is arranged in an air flow of down flow, and a mechanism portion h is located under the disk-shaped object a to prevent dust produced by the mechanism portion h from flying up, by which dust is prevented from affecting the delicate processing operation, and the quality is prevented from being degraded.
When a vacuum vessel i communicating with the reaction chamber, as shown in FIG. 7, is used, the mechanism portion h is arranged under the vacuum vessel i, and the rotating stage c is located in the vacuum vessel i from the downside. In this case, it is necessary to seal a portion that a rotating shaft j of the rotating stage c passes through to prevent leakage when a vacuum is produced in the reaction chamber. For this purpose, a portion of the vacuum vessel i that the rotating shaft j passes through is covered with bellows k. Specifically, one end of the bellows k is connected to the circumference of the opening of the vacuum vessel i that the rotating shaft j passes through, and a vacuum seal m connected to the other end of the bellows k and the rotating shaft j are in slidable contact with each other while maintaining airtightness. Thereupon, the aforementioned necessary positioning can be performed by turning the rotating shaft j and moving it in the direction perpendicular to the axis thereof without the occurrence of leakage under vacuum.
However, in the conventional sealing construction using the bellows k as shown in FIG. 7, which is used for positioning in the vacuum vessel, the slidable contact portion between the vacuum seal m and the rotating shaft j is located in the vacuum region, so that dust produced here adheres to the wafer, resulting in the adverse effect of dust on the delicate processing operation and the degraded quality. Also, such a sliding portion is liable to be damaged and has a low physical life. If any trouble occurs, a vacuum break is caused, and the reliability as the wafer positioning mechanism is decreased. Further, the bellows k must have rigidity for overcoming a restoring force such as to be straightened by the vacuum in the direction such that the misalignment relative to the rotating shaft is eliminated and a deformation caused when following the movement in the direction perpendicular to the axis for the positioning of the rotating shaft j. This following action of the bellows k causes a load when the rotating stage c is moved in the direction perpendicular to the axis to perform the positioning, so that a design is required such as to satisfy the positioning rigidity requirement for overcoming this load, resulting in increased weight and size of the apparatus and therefore an increased cost. An object of the present invention is to provide a method and an apparatus for positioning a disk-shaped object, in which the life of a sealing portion is prolonged by using bellows, and the generation of dust and the effect thereof are prevented.
To attain the above object, with the method for positioning the disk-shaped object in accordance with the present invention, to position the disk-shaped object by supporting a disk-shaped object by a support member which can be rotated and moved in the direction perpendicular to the axis of the rotation, and by moving the support member from the outside of a vacuum vessel, the support member is extended to the outside of the vacuum vessel through an opening of the vacuum vessel and bellows one end of which is connected to the circumference of the opening without being in contact with the opening and the bellows and with a play such that the aforesaid movement can be performed, and the support member is received in a bulkhead portion by a roller bearing so as to be capable of rotating as described above, said bulkhead portion connected to the other end of the bellows and closing the other end of the bellows of a bearing support. The leakage under vacuum can be prevented by sealing the opening of the vacuum vessel that the support member passes through by using the bellows and the bulkhead of the support member, and at the same time the support member can be supported so as to be capable of rotating by eliminating a sliding portion located in the vacuum region by using the bulkhead and the roller bearing at the sealing portion, so that the decrease in life of the sealing portion caused by the sliding portion, the generation of dust, and the adhesion of dust to the object being positioned can be avoided.
Moreover, since necessary rotation is given to the support member from the outside of the bulkhead of the support member via a pair of inside and outside magnetic couplings facing each other on the inside and outside of the bulkhead in a state in which the play is present between the support member and the bellows, and movement in the direction perpendicular to the axis is given to the support member by moving the support member from outside in the direction perpendicular to the axis with respect to the vacuum vessel, the movement necessary for positioning is achieved while the sealing state and the non-contact state between the support member and the bellows are maintained, by which the positioning of the disk-shaped object can be performed.
By optically detecting the orientation and position of the disk-shaped object through a light transmitting window from the outside of the vacuum vessel to position the disk-shaped object, a detection mechanism needs not penetrate the vacuum vessel, so that sealing required by the penetration is unnecessary. Therefore, this configuration is especially suitable in the case where the detection mechanism is moved for detection.
The center position of the disk-shaped object can be detected if at least three positions at the outer periphery thereof are detected or at least two positions are detected when there is information about the diameter. Even if the movement in the direction perpendicular to the axis for positioning is unidirectional, unless a detected center position deviates from the diameter line in said direction, positioning can be effected by moving the disk-shaped object in said direction by a distance of deviation. If a detected center position deviates from the diameter line in said direction, positioning can be effected by performing the same operation after the disk-shaped object is turned so that the detected center position comes onto the diameter line. Even when it is desired to turn the disk-shaped object by supporting the center position by the support member to determine the orientation of the disk-shaped object, there is no problem because the supporting of the disk-shaped object by the support member may be tried again so that the support member is located at the center of the disk-shaped object after positioning the center position. The movement in the direction perpendicular to the axis for positioning may be once, so that the chances of occurrence of troubles associated with positioning and operation errors are reduced, and the reliability is improved. Also, both of the direction and frequency in and of which the bellows follow the positioning while being deformed are reduced. Since the necessary rigidity is reduced along with the positioning mechanism, the reliability and service life are further improved. Also, the apparatus for realizing this can be simplified and made compact and less costly.
In order to support the disk-shaped object once more by the support member as described above, after the once supported disk-shaped object is placed on an auxiliary tray to be separated from the support member and the movement in the direction perpendicular to the axis for the positioning is performed, the disk-shaped object on the auxiliary tray needs be lifted again by the support member whose position has been adjusted. For this purpose, it is preferable to perform the positioning by giving necessary vertical movement to the support member by moving the bearing support in the direction of the axis with respect to the vacuum vessel. The vertical movement of the support member gives convenience in other aspects.
The apparatus for positioning a disk-shaped object in accordance with the present invention is characterized by comprising a vacuum vessel; a support member for supporting the disk-shaped object by extending into the vacuum vessel from the outside and for positioning the disk-shaped object by the rotation, vertical movement, and movement in the direction perpendicular to the axis of the rotation; bellows one end of which is connected to the circumference of an opening that the support member in the vacuum vessel passes through so as to be capable of moving as described above without contact and which has a play such that the support member can move as described above without contact; a bearing support which has a vessel-form bulkhead extending downward and closing the other end of the bellows by being connected to the other end of the bellows, and receives the support member in the bulkhead by using a roller bearing; a moving base which is supported so as to be capable of moving in the direction perpendicular to the axis with respect to the vacuum vessel, and supports the bearing support so as to be capable of moving in the direction of the axis; first driving means for rotatively driving the support member on the bearing support via inside and outside magnetic couplings facing each other on the inside and outside of the bulkhead; second driving means for moving the bearing support together with the support member on the moving base in the direction of the axis with respect to the vacuum vessel; and third driving means for moving the moving base together with the bearing support on a fixed side common to the vacuum vessel in the direction perpendicular to the axis with respect to the vacuum vessel.
The rotation, vertical movement, and movement in the direction perpendicular to the axis of the support member are performed appropriately through the inside and outside magnetic couplings and the first and second support members by using the first, second, and third driving means. Therefore, the above-described characteristic positioning method can be realized automatically with high accuracy on the basis of guiding the support member to the bearing support by using the roller bearings and guiding the first and second support members by using the linear guides.
If the first driving means transmits the rotation of a motor on the bearing support to the outside magnetic coupling, and the third driving means transmits the rotation of the outside magnetic coupling to a cam provided on the bearing support through an electromagnetic clutch in order for movement in the direction perpendicular to the axis, and cooperates with a cam follower provided at a predetermined position on the fixed side, the motor can be used as drive source for both of the first and third driving means, so that the chances of occurrence of troubles and operation errors are reduced and the reliability is improved according as the necessary number of drive sources decreases, resulting in a simple and lightweight apparatus and reduced cost. Also, a configuration in which the rotation is converted into the movement in the direction perpendicular to the axis by the cam and the cam follower offers an advantage that the mechanism is compact and the movement can be controlled with high accuracy.
Other objects and features of the present invention will be apparent from the following detailed description and the accompanying drawings.